以轴对称收扩喷管为基础，利用截面曲率控制的方法并结合流量匹配原则，设计生成了不同出口形状的双S弯喷管。采用CFD数值模拟技术获得了6种模型的流场特征及组分浓度分布，在此基础上利用逆向蒙特卡洛方法对其进行了红外辐射特征研究，先后对比了不同模型的后半球红外辐射强度空间分布、探测面辐射亮度分布以及后半球锁定距离空间分布。研究结果表明：双S弯喷管能够有效减缩目标红外信号，出口形状对排气系统红外辐射有一定影响,梯形出口模型的红外辐射强度明显低于矩形出口以及椭圆出口模型，相比基准模型至少使红外辐射峰值减缩70%；随着梯形下底角的减小，其红外辐射强度逐渐降低；在推力损失可接受范围内利用合适的梯形出口能进一步降低排气系统的红外辐射强度。

Several double-S nozzles with different outlet shapes were designed based on an axis-symmetric nozzle to analyze influence of the outlet shape on the infrared radiation(IR) characteristics of exhaust system. The curvature regulation method and mass-flow matching principle were adopted in the design. The distribution of the characteristics of flow field and mass fraction of six exhaust system models were obtained by CFD. The IR characteristics of these models were calculated by reverse Monte-Carlo method (RMCM), and then IR intensity space distribution of the rear hemisphere, radiation brightness distribution and the lock distance of the rear hemisphere were researched. The results show that, the double S-shaped nozzle can reduce the infrared signal of target effectively. The outlet shape can affect the IR characteristics of exhaust system. The models with trapezoid outlet shape has significantly lower IR intensity than the double S-shaped nozzles with other outlet shapes, and can reduce the peak of IR intensity at least 70% compared with the axis-symmetric nozzle. Reducing trapezoid′s bottom angle can enhance the infrared suppression effect, and appropriate outlet shape can further suppress the IR intensity of exhaust system within acceptable thrust loss.